fix CI for new Ubuntu image

Author: SethTisue

.github/workflows/ci.yml

@@ -21,5 +21,6 @@ jobs:
       with:
         distribution: temurin
         java-version: ${{matrix.java}}
+    - uses: sbt/setup-sbt@v1
     - name: Test
       run: sbt ++${{matrix.scala}} test proj/headerCheck package